The use of endoscopes and similar medical instruments for diagnostic and therapeutic applications is well known in the art. Such devices are used for viewing virtually anywhere within the body. To eliminate the problems of cleaning and sterilizing these instruments between uses, it is known to cover these devices during use with sealed, protective sheaths, sleeves and covers of various sorts. Such sheaths are commonly elongated, tubular sleeves each having one open end for inserting the medical instruments and one closed, distal end. After use, the protective sheath is removed from the instrument and discarded. Thus, the cost of the protective sheath is an important factor in its utilization.
The protective sheath, however, must also meet several demanding requirements for safety and optimal effectiveness, and satisfying these standards has typically led to relatively high costs of production. First, because the endoscope often must be inserted far inside bodily cavities, the protective sheath must be relatively long in order to completely cover all of the endoscope that is inside the body. Of course, the sheath must also be made of a material that is non-toxic and substantially inert to bodily fluids.
Because the endoscope sometimes must be bent or snaked around bones, organs or other bodily obstructions to reach the desired internal location, it is desirable for the sheath to have some degree of flexibility. At the same time, for some applications, the sidewalls of the sheath should be relatively inelastic to avoid stretching or distortions while in use, which could lead to rupture of the sheath or to damage to the body. For similar reasons, for some applications, the internal diameter of the protective sheath should be larger than the diameter of the medical instrument, but should not be larger than required to accommodate the instrument.
Up to now, it has not been possible to prepare protective sheaths of adequate lengths, having very small internal diameters, and also having the desired balance between flexibility and inelasticity of the sidewalls. All of the protective sleeves currently in use are lacking in one or more of the following desirable characteristics: (1) optically transparent, thin-walled viewing "window"; (2) thin, flexible but relatively inelastic sidewalls; (3) smooth transitions and corners; (4) reliability--i.e. no leaks; and (5) easy and inexpensive to manufacture. Specifically, it is impossible to obtain lenses with side walls of almost any length and with sidewall thicknesses less than about 0.015 inches using conventional injection molding techniques, especially if optical transparency and high strength are important. Furthermore, injection molding requires a draft or taper along the sidewalls in order to eject the finished product from the mold. Vacuum-forming or thermoforming is another technique that can be used to produce clear packaging. However, this process generally results in relatively thick walls, generously-radiused corners, and, again, substantially tapered sidewalls.
In addition, because an endoscope is an optical instrument, the protective sheath must include at least one optically transparent viewing "window" at or proximate to the closed, distal end of the sheath and in alignment with the light source and window of the endoscope. The location of the optically transparent window of the sheath will depend, in part, on whether it is to be used with an end-viewing or side-viewing endoscope. In order to maintain optical transparency and minimize visual distortions, it is desirable that the viewing window of the sheath be substantially inelastic. At the same time, as with the sheath sidewalls, some degree of flexibility in the sheath window is desirable to facilitate maneuvering the sheath and endoscope through the body and, in many cases, helping to keep the window tight against the endoscope. Whereas glass lenses are optically transparent, they are even thicker than available plastic lenses, are rigid and non-deformable, and present a potential shattering hazard, especially when made thin.
In the prior art, as discussed below, it is typical to fashion the sheath window independently of the sheath and subsequently join the two elements using adhesives or thermal bonding. Obviously, this two-step process is relatively costly and time-consuming. This two-step manufacturing process also increases the risk of sheath failure along the bonded edge. All of the prior art endoscope covers also all have thick, rigid glass or molded plastic lenses and/or sidewalls that make these devices heavy, bulky and of limited utility. They cannot be used, for example, with most small endoscopes in small body cavities, especially because the adhesive joints also add to the thickness or diameter of the final unit. Thus, present technology can produce covers for endoscopes, but these covers substantially limit the performance of the instruments, especially those with very small diameters.
Typical of the prior art in this field are U.S. Pat. Nos. 4,646,722 (Silverstein et al.) and 4,907,395 (Opie et al.). The Silverstein et al. patent teaches the use of an endoscope sheath comprising a flexible tube surrounding the elongated core of an endoscope. The flexible tube has a transparent window near its distal end positioned in front of the viewing window of the endoscope. As seen in FIG. 2 of this patent, the sheath comprises a cylindrical support body 30 having a viewing window 32 mounted at one end and a roll of elastomeric material 48 secured to support body 30.
An alternative embodiment of the Silverstein et al. sheath for use with side-viewing endoscopes is shown in FIG. 10. In this embodiment, the sheath 110 comprises an end cap 112 of relatively rigid material mounted at the end of a flexible cylindrical tube of elastomeric material 114 formed into a roll 116. The end cap 112 includes a pair of transparent windows 118, 120. Although the Silverstein et al. patent does not describe how viewing window 32 is fastened to support body 30, or how viewing windows 118, 120 are fastened to end cap 112, it is clear that these are separate and distinct components which are not formed continuously integral with the elastomeric tube. The later Opie et al. patent is essentially an improvement invention directed to a method of packaging and installing the endoscope sheaths of the Silverstein et al. patent.
U.S. Pat. Nos. 3,794,091 (Ersek et al.) and 3,809,072 (Ersek et al.) are directed to sterile sheaths for enclosing surgical illuminating lamp structures that have elongated light transmitting shafts. The sheaths in Ersek et al. are fabricated from films of flexible plastic material, such as vinyl tubing, polyethylene or polypropylene. The method of fabrications, however, is not disclosed. Ersek et al. prefer a wall thickness of between three and six mils for the required durability, rigidity and transparency. The tip end portion 20 of the sheath is described as a "generally rigid lens element" sealed to the sheath in a continuous sealing line 21 by thermal welding or adhesive bonding. Here again, it is clear that the tubular sheath portion 22 and lens element 20 are separate and distinct components which are not formed continuously integral with one another. More importantly, the lens element here is rigid and thick.
U.S. Pat. No. 4,957,112 (Yokoi et al.) describes an ultrasonic diagnostic apparatus, the distal end portion of which includes a cover 24 made of a thin, hard, polyethylene sheet that has a window portion 34 along a sidewall. At col. 4, lines 55-58, Yokoi et al. describe window 34 as being "integrally formed" with the cover 24 for permitting the passage of an ultrasonic wave from the end of the instrument. Thus, window-34 need not be optically transparent; and, cover 24 covers only a relatively small distal portion of the diagnostic instrument.
U.S. Pat. No. 4,878,485 (Adair) describes a rigid, heat sterilizable sheath S that provides an outer casing for a video endoscope. The sheath includes a viewing window 32, a flat disc positioned at the distal end positioned in the optical path of the endoscope. Window 32 is described as a "rigid" cover made of glass, sapphire or polycarbonate. Once again, it is clear that cylindrical housing 30 and window 32 are separate components, and that the lens is thick and rigid.
U.S. Pat. No. 4,819,620 (Okutsu) describes an endoscope guide pipe which is rigid and formed from a transparent material such as glass or plastic. In one embodiment shown in FIG. 6, a pair of slots in the sidewall of the guide pipe is filled with a transparent material, such as glass, to define a window section 12f.
U.S. Pat. No. 4,470,407 (Hussein) describes a flexible, elongated tube with an elastomeric balloon sealingly mounted at the distal end of the tube for enclosing an endoscope. Inside the body, the balloon can be inflated to facilitate endoscope viewing. At col. 5, line 60-col. 6, line 22, Hussein describes a process for forming the balloon in which a polished aluminum mandrel is dipped into a latex formulation that is subsequently cured. FIGS. 4 and 5 show an alternative embodiment in which a tubular stem portion of the balloon 118 surrounds and extends substantially along the length of tube 114. In either case, the tube and the balloon are separate components.
U.S. Pat. No. 4,201,199 (Smith) describes a relatively thick, rigid glass or plastic tube 10 which fits over an endoscope. The distal end of the tube in the Smith patent is provided with an enlarged, sealed bulb 12 having a radius of at least 3-4 mm to reduce optical distortion caused by a too-small radius of curvature. Although the bulb 12 is formed continuously integral with tube 10, the rounded bulb is rigid, inflexible, thick-walled, and does not yield the same degree of distortion-free optical transparency as a substantially flat window.
U.S. Pat. No. 3,162,190 (Del Gizzo) describes a tube 19, made from molded latex or similar material, through which an optical instrument is inserted. Viewing is through an inflatable balloon element 24 mounted at the distal end of the tube. Finally, U.S. Pat. No. 3,698,791 (Walchle et al.) describes a very thin, transparent microscope drape which includes a separately formed, optically transparent, distortion-free lens for viewing.
Thus, the prior art patents describe endoscope sheaths that suffer from one or more of the following disadvantages: being comprised of separate sleeve and window elements that must be bonded together, having relatively thick and/or rigid sleeve sidewalls, having rounded or elastomeric windows that result in optical distortion, and having relatively thick and rigid and/or breakable windows. These and other problems with and limitation of the prior art are overcome with the protective sheath apparatus of this invention. In particular, the method of this invention produces a sheath having a thin-walled, close-fitting sleeve with a closed, distal end comprising a thin, substantially inelastic, optically transparent window formed continuously integral with the sidewalls of the sleeve, or with a portion of the length of the sleeve, and shaped to conform with the viewing window of an endoscope.